[Eddie H.]

I have a 69 GMC long bed, and if I see anything north of 12 to 13 mpg, I'm extremely happy.

With the original 307 it would get 8 to 10. I built a mild small block 400, and put in it and can get 12, and sometimes 13 on a really good day.

The 307 was straining to push a 4500 pound truck with the aerodynamics of a shipping container down the road at 65 mph, where the 400 isn't even breathing hard, so it uses less fuel.

300 HP and 30 MPG is near impossible for one of these trucks, no matter what engine /transmission you use.